The present invention relates to translational bearing structures which are particularly useful in optical instruments such as Fourier transform infrared spectrophotometers.
In such instruments, in order to obtain accurate results, it is extremely important to provide for frictionless movement and positional control of a scanning mirror in a translational (nonrotational) mode. During such movement, the mirror must remain at precisely the same angle to the direction of racy translational movement, preferably substantially perpendicular to such movement. The accuracy of this alignment must be maintained to within very small tolerances, such as in the order of eight millionths of an inch per inch. That is, for a one inch wide reflector, the tilt of one edge with respect to the other must not exceed eight millionths of an inch.
In order to obtain such a high degree of accuracy without friction, it has been thought to be necessary to employ a rectangular cross-section air bearing to permit translation without rotation. However, a rectangular cross-section air bearing which is capable of such high accuracy must be machined very carefully, and with high accuracy, and has been found to be relatively expensive to produce.
Accordingly, it is one object of the present invention to provide an improved frictionless translational bearing for an optical instrument element which maintains a high accuracy and which is greatly reduced in cost.
It has been known that one approach to reducing the cost of a frictionless translational bearing might be to employ a circular cylinder air bearing instead of a rectangular bearing. However, when a cylindrical air bearing is employed, it is essential to restrain the bearing from rotation, or to precisely control the rotation of the bearing. This has been a difficulty in prior attempts to employ circular cylinder air bearings for such purposes. However, no truly satisfactory arrangement has been devised for the utilization of a circular air bearing.
Accordingly, it is another object of the present invention to provide an improved frictionless translational bearing for an optical instrument element which satisfactorily employs a cylindrical air bearing together with a frictionless means for preventing rotation of the optical instrument element carrier.
Further objects and advantages of the invention will be apparent from the following description and the accompanying drawings.